Glow indicator lamp



March 1935- J. A. LINDER ET AL 1,993,012

GLOW INDICATOR LAMP Filed June 5, 1951 INVENTORS J34. L/NDER 6.4.35 Gfll/GUZf/r ATTORNE Patented Mar. s. 1935 UNITED STATES PATENT OFFICE GLOW INDICATOR LAMP tion of Pennsylvania Application June 3, 1931, Serial No. 541,772

Claims.

This invention relates to incandescent electric lamps operated in series and relates more particularly to a combined incandescent filament and glow discharge lamp wherein the glow discharge 5 serves to indicate a failure of the filament of the lamp.

Certain types of incandescent electric lamps such for example as those employed for Christmas tree lighting and which may be termed miniature lamps, are operated when a given number are connected in series so that the combined voltage of the lamps equals the line voltage supplying the electrical energy.

It has been found that when using a plurality of lamps connected in series, considerable inconvenience occurs upon a failure of one of the lamps, as for example, when a filament breaks or burns out, such failure interrupts the continuity of the circuit and the rest of the lamps are extinguished.

When a string or a plurality of series connected lamps become extinguished owing to a failure of one of the lamps, it is difilcult to determine by inspection which lamp is defective and it becomes necessary at the expense of time and trouble in order to discover the lamp which has failed, to test by trial until the defective lamp is found.

Various methods have been proposed to overcome the above disadvantages and lamps have been provided with cut out material so that the cut out material would carry the load when a lamp failed, permitting the remaining lamps to burn, thus indicating the defective lamp.

In copending application Serial No. 502,052 filed December 13, 1930 by W. E. Anderson and in Patent No. 1,893,305 issued January 3, 1933 to H. C. Rentschler which applications are assigned to the assignee of the present invention, a lamp and method of making are shown and described wherein the use of cut out materials is avoided and the lamp is so constructed that when the filament fails a glow discharge will occur within the lamp which glow discharge by reason of its visibility will clearly indicate the otherwise defective lamp.

The above mentioned copending applications set forth certain methods or modes of manufacturing a lamp of the character described wherein a material is introduced to reduce the voltage drop between electrodes within the bulb to effect a glow discharge at the ordinary commercial voltages.

It is an object of the present invention to provide a lamp capable of producing a glow discharge upon a failure of the filament and particularly in providing a means for more emciently and effectively supporting a material for reducing the voltage drop.

Another object of the invention is toprovide a 5 lamp of the character described in which an active metal may be readily applied to lead wires of a lamp to make the leads convertible into electrodes to sustain a glow discharge upon a failure of the filament of the lamp.

Another object of the invention is to provide means for more expeditiously and economically applying an active metal to metallic conductors to constitute electrodes.

Another object of the invention is to provide a binder for an active metallic powder to facilitate the application of the powder to metallic conductors and in which the binder acts as a getter to clean up residual impurities.

Other objects and advantages of the invention will be more fully understood from the following description together with the accompanying drawing, in which Fig. 1 shows a lamp with the bulb in section and in which the support or lead wires are coated with an active material in accordance with the present invention;

Fig. 2 is an enlarged viewtaken on lines 11-11 in Fig. 1 and Fig. 3 is a diagrammatic view of a number of lamps in series and shows one of the filaments broken and indicates a glow discharge between the prepared support wires which serve as electrodes.

Although the present invention may be applied to various types of electrical devices where it is desirable to produce a glow discharge upon the failure of a current carryin element a selected embodiment of the invention may comprise a bulb 10 having a. mount 11 secured therein by butt sealing in the usual manner. The mount may comprise conductive support members or lead wires 13 and 14 held in given space relation by a glass bead 15. The upper ends of the lead wires are secured to the terminals of a coiled filament 16 and the usual base 17 may be secured to the bulb. v

The lamp shown is of the type commonly used for Christmas tree lighting and it is desirable in such lamps to have some means for indicating the failure of the filament.

For the purpose of converting the incandescent electric lamp as shown, into a glow lamp upon a break or failure of the filament, electrodes are provided of an active metal 18 such as mag- 65 nesium, aluminum or thorium or a mixture of such metals and in accordance with the present invention one of the said metals or a mixture thereof is used or applied in the presence of a binder such as a sodium silicate solution or potassium silicate, potassium chloride or sodium chloride may be used in combination with sodium silicate or nitro-cellulose.

The metal and the binder may be mixed together and applied as a paste to the leads or the binder may be applied first to the leads and the leads may then be dipped in the powdered metal which adheres to the binder.

When the lead in wires or metallic conductive supports are provided with the coatings of a metal as for example magnesium, the electrode drop is lowered so that if the filament breaks or otherwise fails the line voltage impressed across the electrodes will result in a glow discharge thus indicating, by reason of the visible glow, the lamp in which the filament has failed and the same may readily be replaced by a new lamp.

By using a sodium silicate solution as the binder the getter action of the sodium silicate is utilized to clean up residual impurities since the sodium silicate reacts with the active metal and tends to keep the gas clean even though the discharge taking place between the electrodes tends to liberate impurities and the sodium would also serve to aid in lowering the electrode potential as long as it is present on the electrodes.

It has been found that a binder of sodium silicate in addition to serving to hold the magnesium to the lead wires serves to clean up the neongas and produce a condition tending to make the lamp glow on volt circuits. N0 definite explanation is advanced for this action but it does not appear to be the usual action that is caused when sodium silicate is used solely as a clean up agent. The result attained seems to be caused, at least partially, by reaction with the magnesium causing a liberation of sodium vapor. Evidence of this reaction is evinced by a sputtering which occurs sometimes after the filament has failed. This so-called sputtering is in reality a glow caused by discharge between the two electrodes which give off the characteristic sodium color. Moreover, when such a sputtering is seen the electrical characteristics of the lamps change very appreciably and the current flowing through a circuit of one of these lamps connected in series with seven other lamps which have not failed on 115 volts again indicate the presence of sodium vapor in the lamp having the glow. There are other indications that some such action goes on, but apparently to a lesser extent during the life of the lamp and before the filament has failed, such indication occurs when an induction coil is allowed to discharge through the gas in the lamp.

It will be evident from the above that the sodium silicate serves not only as a binder but in combination with the magnesium serves to condition the neon to facilitate the glow at the given voltage. I

It has been found that when a lamp is made in accordance with the present invention and the magnesium in a binder of sodium silicate is deposited on the leads, the initial burning of the lamp serves to radiate heat to cause a reaction of the sodium silicate so that gases are liberated and the surface of the magnesium is freed from oxide or otherwise rendered effective to produce the low voltage break down necessary in a lamp of the present type.

It will be understood that when using magnesium or similar material considerable difilculty is experienced in obtaining a clean surface and as described in above mentioned copending application Ser. No. 502,077 the magnesium is vaporized within the bulb to obtain an oxide free surface to give the desired reduced voltage drop. In the present invention this desired condition is attained by the use of the binder when subjected to heat radiated from the filament so that after a lamp has been in use several hours the condition of the electrodes, insofar as their effectiveness in giving a low voltage drop is concerned, is improved.

In constructing a lamp in accordance with the present invention it is preferable to provide the lamp with lead wireshaving portions thereof spaced about two millimeters apart on centers. A metallic powder such as magnesium powder of 200 mesh is mixed with a binder made ofequal parts of water and U grade sodium silicate solution, or the binder, that is, the sodium silicate solution may be applied to the leads and the active metallic powder dusted thereon so that it adheres to the binder. The sodium silicate above mentioned known as U rade contains 32.9 SiOHilicate, 13.7 Naz-O sodium oxide, specific gravity about 1.55. It is preferable when applying the material in the form of a paste composed of a metallic powder and sodium silicate to apply the paste to portions of the leads a few millimeters above the bead 15 and about a millimeter from the ends of the leads. a

The leads may be bent half way between the bead and the tips so that they are about 1 or 2 millimeters apart on centers and at normal spacing at the tips. Good results have also been obtained with the leads bent so that they were about 1 millimeter apart at their centers and with the portions between the bead and the tips parallel.

In connection with the use of the above metallic material as electrodes, it has been found that satisfactory results are obtained when the lamps are filled with a mixture of 99.5 per cent 01 neon and .5 per cent argon at about 25 millimeters pressure, although other gases or combinations thereof may be employed. Lamps made in accordance with the above give satisfactory results when burned on the ordinary line voltage of 115 volts.

Although sodium silicate is preferable as a binding material, other binders as for example a nitro-cellulose binder may be employed although some discoloration results which, however, may not be suflicient to cause serious disadvantage particularly when using a lamp having the bulb coated with a light diifusing material.

The present invention makes it possible to provide an incandescent lamp with electrodes which will lower the voltage dropwhen the filament breaks as at 20 in Fig. 3 whereupon a glow 21 discharge occurs and gives a visible indication of such break.

Although the invention is shown and described as applied to a miniature or Christmas tree lamp, it is obvious that the same may be used in connection with other types of lamps and the various modifications may be made in the method and arrangement without departing from the spirit and scope of the appended claims.

What is claimed is:

1. An incandescent electric lamp comprising a bulb, an ionizable medium in saidbulb, a filament, a pair of metallic support members for said filament and magnesium powder in a binder of sodium silicate deposited on portions of said support wires to constitute electrodes.

2. An incandescent electric lamp comprising a bulb, an ionizable medium within said bulb, a

filament, lead wires for said filament, a getter material disposed on said wires and a deposit of magnesium on said material for lowering the voltage drop between said wires to produce a visible glow discharge when full voltage is applied between said wires upon a failure of said filament.

3. An incandescent electric lamp comprising a bulb, an ionizable medium within said bulb, a filament, lead wires for said filament, a deposit of magnesium on said wires and a sodium silicate binder for said magnesium to provide electrode surfaces of low voltage drop to ionize said gas and produce a glow upon a failure of said filament. Y

4. An incandescent electric lamp comprising a bulb, an ionizable medium in said bulb, a filament, lead wires for said filament, said lead wires having portions disposed in relatively close space relation, and a deposit of a getter material on said portions and a material deposited on said getter for lowering the voltage drop between said wires to ionize said medium when the full lamp voltage is applied to said portions upon a failure of the filament.

5. An incandescent electric lamp comprising a bulb, a gas ionizable to give a visible discharge at the voltage of the line on which the lamp operates, a filament, lead wires for conducting electrical energy to said filament, a mixture of magnesium and a binder deposited on portions of said lead wires within said bulb to clean up residual gas and lower the voltage drop therebetween whereby a visible glow is produced when the-line voltage is impressed between said por- 20 tions.

JOHN A. LINDER. CHARLES L. E. DE GAUGUE, JR. 

